The invention relates to a method for feeding hydroforming presses (internal high pressure forming presses) in order to produce workpieces which are composed of a plurality of parts, preferably camshafts, in a hydroforming process which is known per se. The hydroforming process is used to nonpositively and positively connect cam rings and also other components, such as drive elements, to one another. The hydroforming press which carries out the method is equipped to receive at least one workpiece, i.e. a camshaft which comprises a hollow shaft with the cam rings which are to be applied to it.
The hydroforming process generally changes the geometry and dimensions of workpieces which are hollow through the action of a pressurized medium (air, liquid). These axial forces deform the workpiece to the extent which is predetermined by the mold, also known as the mold nest, in the hydroforming press.
Hydroforming presses of this type have two dies, a lower die and an upper die, the mold nests of which, in the closed state, correspond to the shape of the overall workpiece, the camshaft with the cam rings arranged appropriately. In general, the die is parted in the center.
There are various known designs of hydroforming processes and their dies, but these all operate according to the same principle. The workpieces which are to be treated are put in place and the internal pressure deforms them. It is preferable to produce rotationally symmetrical workpieces. The process itself, the hydroforming operation, takes place in an extremely short time, but the ancillary times, in particular the feeding of the hydroforming press, are lengthy, which ultimately means that the cycle time is long.
It has already been attempted to produce camshafts from a hollow shaft and cam rings secured to it. In this case, the loading time is very long, since the cam rings have to be placed very accurately in their position, i.e. in accordance with their subsequent function, and their position (angular position) must not change as a result of the shaking and vibrations which occur in the hydroforming press. An additional factor is that the position of some cam rings, on account of their shape, is very labile, and in particular these rings are at risk of changing position. Even if a correct, functionally appropriate position of the cam rings is checked using gauges or other checking means after they have been placed into the hydroforming press, it is impossible to rule out the possibility of the position changing when the die is closed. A change in position of just one cam ring has serious consequences. The cam rings are hardened, and if they are incorrectly positioned in the mold nest they will destroy the die and will also be damaged themselves, rendering them unusable. Since the dies are very expensive, damage of this nature is to be ruled out at all costs. Since the aim is to increase the productivity of hydroforming processes, the dies are also designed in such a way that they receive a plurality of workpieces. Of course, there are limits on this expansion, since the supply and control of the pressurized medium entails further measures and increased outlay, which in turn increases the costs of the hydroforming press and ultimately also the process costs.
These drawbacks do not occur to such an extent in the case of deformation of simple, rotationally symmetrical workpieces, but do so more with complicated workpieces, such as camshafts, which on account of their function require a very high degree of accuracy. Slight changes in the position of cam rings even just as a result of the force of gravity, which has a particularly critical effect in connection with machine vibrations when the cam rings are positioned with the tip of the cam facing upward and in an angle which deviates from the vertical, have to be eliminated, and this is almost impossible with the known methods used to feed the hydroforming press.
DE 36 43 803 A1 discloses an assembly apparatus for assembled camshafts, and assembly methods. The document discloses a mounting apparatus for assembled camshafts, having a holding apparatus for axially fixing individual elements, such as cam disks, bearing seats or gearwheels, and a pressure-medium sensor for hydraulically widening a hollow shaft in sections in which the elements and the hollow shaft are connected to one another in a nonpositive manner. Individual fixing disks are provided for the holding apparatus, each having a central opening for receiving one of the elements, such as cam disks, bearing seats or gearwheels, and an external bearing seat for being received in each case in one bearing location of the holding apparatus. The individual elements can be fixed at the appropriate angle prior to mounting by means of these fixing disks, while the hollow shaft can execute radial movements with respect to the individual elements. This known mounting apparatus therefore comprises a lower part and an upper part, with identical mold nests for receiving parts being formed in the lower part and upper part and the lower part and upper part being connected in an accurately fitting manner. Positioning elements are arranged on the upper and lower parts at the locations in the upper part and/or lower part where it is necessary to secure the parts in position, these positioning elements ensuring that the upper and lower parts are connected to one another in an accurately fitting manner.
Furthermore, the laid-open specification cited above discloses a method for assembling a camshaft. In this method, all the parts of the camshaft are placed into the lower part of a mounting device, which comprises a lower part and an upper part, in a positionally and functionally correct manner; the spatial and functionally correct position of the parts is checked; the upper part of the mounting device is placed onto the lower part; the parts are nonpositively and positively connected in the predetermined position in the mounting device by clamping; the upper part of the mounting device is then, together with the parts held therein, put down on the lower die in the precisely defined position by means of positioning elements.
The invention is based on the object of providing a method for feeding hydroforming presses which allows a workpiece which is not rotationally symmetrical and is composed of a plurality of individual parts, preferably a camshaft, to be produced in a known hydroforming process, while ensuring the high degree of accuracy required with regard to the position of the cam rings. Furthermore, it is intended to significantly reduce the ancillary time required to feed the hydroforming press, in order to increase the productivity of the method and of the hydroforming presses. A further increase is also to be made possible by virtue of the method being configured in such a way that a plurality of workpieces can be produced in a single cycle. The method is intended to rule out the possibility of the workpiece and/or parts thereof and the hydroforming press being destroyed or damaged.
The basic structure and operation of the hydroforming press are to be retained and matched to the method according to the invention without any significant increase in costs. The device for carrying out the method is to form part of the hydroforming process, i.e. it is to be functionally connected to the hydroforming press in such a manner that the overall hydroforming process can be carried out more economically. The device is to form an indirect part of the hydroforming press and is to be used directly for carrying out the method.